In the following description the term “rover” is applied to moveable receivers, whether they are attached to moving rovers or are otherwise moved about from time to time.
In some applications it is desirable for rovers to monitor their positions and this is usually accomplished by receivers, e.g., GPS or GLONASS receivers, which calculate their positions by means of ranging signals transmitted by earth-orbiting satellites. To provide a position determination in three coordinates, a receiver must receive ranging signals from four satellites, preferably more, to lessen the errors due to noise and multipath distortion. With signals from four satellites, the receiver can calculate the ranging system's time at its location and also its position in three coordinates.
At times a rover may enter an area where trees and/or various other objects impede the signal reception from some of the satellites, thus degrading the accuracy of position determination. Various arrangements have been used to cope with this problem in automobiles, for example, but these solutions are not suitable for some small rovers, such as golf carts moving over golf courses because of, for example, associated costs and complexities. The present invention deals with these situations.